Wireless Personal Area Networks (WPAN) communication systems are extensively used for data exchange between devices over short distances of no more than 10 meters. Current WPAN systems exploit the frequency band in the 2-7 GHz frequency band region and achieve throughputs of up to several hundred Mbps (for Ultra-WideBand systems).
The availability of 7 GHz of unlicensed spectrum in the 60 GHz band and the progress in the RF IC semiconductor technologies are pushing the development of the millimeter-Wave (mmWave) WPAN systems which will operate in the 60 GHz band and will achieve the throughputs of about several Gbps. Currently a number of standardization groups (Institute for Electronic and Electrical Engineers (IEEE) 802.15.3c, IEEE 802.11ad, Wireless HD SIG, ECMA TG20) are working on the development of the specifications for such mmWave WPAN networks. The standards are developed mainly as addendums to the previous WPAN standards with the introduction of new PHY layers and also are trying to reuse most of the MAC functionality. However, the modifications to the MAC layer are also required to exploit specific mmWave WPAN characteristics.
A communication link operating at 60 GHz is less robust due to the inherent characteristics of high oxygen absorption and significant attenuation through obstructions. In order to satisfy the link budget requirement, directional antennas have been envisioned to be used in creating a mmWave communication link.
Even if directional antennas are available, for initial device discovery, association and synchronization, the use of omni (or quasi-omni) beacons is typically required. The way a station (STA) performs an omni directional transmission changes according to the antenna type employed, but the bottom line is that regardless of how it is accomplished, the overhead associated with omni transmissions is very high since omni frames are transmitted at very low data rates (few Mbps) as compared to the multi-Gbps data rates that are used for directional transmissions.
Future mmWave WPAN will widely use directional antennas. The high gain of the directional antennas will be required to achieve the necessary signal to noise ratio (SNR) margins over very wide bandwidth (˜2 GHz) mmWave WPAN links under the limited (˜10 dBm) transmitted power. The high-gain antennas may have to be steerable in order to support arbitrary placement of different devices (e.g. to not be limited to fixed positions).
Thus, a strong need exists for new techniques and improvements in millimeter wave wireless technologies.
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